Ergonomically designed office chairs are commonly configured so that the back can recline alone, the seat and back can recline as a unit, or the back can recline in a coordinated proportion with the seat. The latter are commonly known as “synchro-tilt” chairs. Most of these synchro-tilt chairs have a mechanism that loads a spring as the user reclines and a mechanism for adjusting the resistance to being reclined (also known as tilt or chair tension). In these chairs, the pre-load on the spring requires the user to input a high force or a large displacement in order to make any adjustments to the chair tilt tension. These adjustments often are difficult, awkward or require an extensive amount of user work to generate perceptible changes in the tension. In addition, most of these chairs provide no visual or tactile feedback to the user about the range of tension adjustment available and where, within this range, the chair is currently. As a result, many users don't take full advantage of the versatility of the chair in accommodating their comfort. For example, many of these chairs provide a rotatable knob or handle underneath the seat that includes plus and minus symbols. Rotation of this knob can require 30 revolutions or more to adjust the tension between the lowest and highest available levels.
The force applied to the chair back during reclining, as mentioned above, also may result in a shearing force between the user's back and the chair back. This shearing force may be perceived by the user as a tendency for the chair back to pull out the user's shirt tail, known as ‘shirt pull’ in the industry. In addition, reclining in these types of chairs may also cause a “pull-away” between the chair back and the user's back, such that the chair back does not remain in contact with the user's back as the chair reclines. As a result, the chair fails to provide proper support causing discomfort and dissatisfaction.
In addition to adjustment of the tilt tension, many of these chairs include a tilt lock to prohibit reclining of the chair, a seat height adjustment, arm adjustments, and/or seat position adjustments. Improvements in these other chair adjustments are also desirable to make them more user friendly and thereby encourage the user to take advantage of the various adjustments available to customize the chair for the user's personal comfort or work style.